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Discussion Starter · #1 ·
i dont have any on my car and i dont really want any tbh.

but is it considered unsafe to run twin gt28s at 1.4 - 1.5 bar without dump valves ?

i know the old t series are ok at that boost without dumps but im unsure on the gt series ?
 

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Do you mean VTA dump valves or other after-market types, rather than the standard recirculating ones you possibly have? Or are you saying you've removed them (not a good idea to run without any dump valves)?
 

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rally cars run with no Blow off valves at all, its the rules, as a result their turbos last about a wweek.:chairshot
 

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on ball bearing turbos its suposed to be fine my 3071 ran without one for a while and it was ok roller bearings or thrust bearings are meant to have issues
 

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Keep the recirculating ones, that what Nissan designed for the engine !
 

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Bov's are noise suppression devices afaik.
Many turbo cars run without them, normal cars and race cars.
I haven't seen real evidence that compressor surge kills turbos
 

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rally cars run with no Blow off valves at all, its the rules, as a result their turbos last about a wweek.:chairshot
id like to make people aware that by saying 'blow off valves' i was reffering to both VTA and recircs as a group. :thumbsup:

kev
 

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Can someone enlighten me as to why you'd want to run without one? I'm not trying to be clever, just can't see it; surely it's better to vent away the air 'pressure' when the throttles closed, so that the turbo keeps spinning?

WRC etc. run anti-lag to keep the turbo spinning, so I can see why they need something different.
 

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Discussion Starter · #10 ·
i must have standards on somewhere as i can just here a dump must be recirc valve.
 

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Can someone enlighten me as to why you'd want to run without one? I'm not trying to be clever, just can't see it; surely it's better to vent away the air 'pressure' when the throttles closed, so that the turbo keeps spinning?

WRC etc. run anti-lag to keep the turbo spinning, so I can see why they need something different.
When there's no bov, the pressure will build up and you will hear the compressor wheel chopping air, I don't think that the excess pressure slows down the compressor wheel considerably. However, when you do have a bov, all the pressure in the intercooler and piping that you turbo had to build up is lost and it has to build it up again. I can't remember which ones, but there are turbo engined race cars running without them.
 

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When there's no bov, the pressure will build up and you will hear the compressor wheel chopping air, I don't think that the excess pressure slows down the compressor wheel considerably. However, when you do have a bov, all the pressure in the intercooler and piping that you turbo had to build up is lost and it has to build it up again. I can't remember which ones, but there are turbo engined race cars running without them.
actually the excess pressure (compressor surge) does slow down the compressor wheel considerably, this is the whole point of a relief valve. compressor surge kills bearings and is what knackers the turbo, which is ok for well funded race teams and rally cars but not for normal cars.
when you let off the throttle the presurized air 'bounces' off the throttle and returns towards the turbo as a wave, its this wave that slows the compressor wheel and creates turbo lag because the wheel has to speed up again, if this unwanted pressure was released to the air (VTA BOV) or back into the non-pressurised (recirculating BOV) the compressor wheel whouldnt slow down as much and would reduce lag.

hope this helps.:thumbsup:

kev
 

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i think this is what most of the dump valve producing companies want you to believe.

how long does a gear change last? have you tried pushing air through a turbocharger at 100.000+revs? dont think its going to slow it down too much.

race cars dont use them for a reason.

why would someone say, that race teams dont care for turbos as they are well funded.
breaking a turbo is the difference between wining or loosing, and i dont think they would care too much for the cost or the weight of a valve with a spring.

i cant remember where i saw this, but its on the net somewhere, this guy tested with a turbo wheel sensor the drop in revs during gearchanges with and without valves, and there was close to no difference.

i would love to see any dump valve producer do some tests like this, and use them for publicity. so far none have done.

in my opinion, i think the idea of turbos breaking from surge (presurized air.....basically what they are designed to do) is more of a perfect publicity stunt.
 

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actually the excess pressure (compressor surge) does slow down the compressor wheel considerably, this is the whole point of a relief valve. compressor surge kills bearings and is what knackers the turbo, which is ok for well funded race teams and rally cars but not for normal cars.
when you let off the throttle the presurized air 'bounces' off the throttle and returns towards the turbo as a wave, its this wave that slows the compressor wheel and creates turbo lag because the wheel has to speed up again, if this unwanted pressure was released to the air (VTA BOV) or back into the non-pressurised (recirculating BOV) the compressor wheel whouldnt slow down as much and would reduce lag.

hope this helps.:thumbsup:

kev
Hi Kev,

I understand very well the function of a blow off valve - to relieve pressure from the compressor side of the turbo under closed throtte. It is my opinion that these loads under closed throttle are negligeable and will have near enough to zero effect on turbo life.

Take group C cars, no blow off valve. Take an endurance car at LeMans, it will travel around 5000km in 24hrs. This amount of strain is more than any road car will ever see in on/off throttle state, yet the turbos survive without BOV's. The fastest Group A Ford Sierras in the world never used a bov and had less turbo failures than the bov equipped opposition.

I think the whole argument about response is duff as well - to keep the turbo spinning between gearchanges. If bov's made any difference, they would have been fitted to every turbo car involved in motorsport, but it's not the case.

So far, marketing from companies and people selling such products are the only ones who tell me I need a bov, I really believe my turbo spins fine, especially at the kind of boost I'm running (0.85bar).
 

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so why did nissan fit recirculating BOVs? if they do nothing to benefit the car then why bother? im not praising aftermarket BOVs im saying a pressure relief valve is fitted for a reason! would you recommend i just bung mine up?

kev
 

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Discussion Starter · #16 ·
100 % dump valves increase lag ive tried it, as does a bigger intercooler well 3 times bigger on my test ! but dump valves must improve turbo life.

ive had lots of cosworths but all on either t3, t34 and t35 and 2 t4 cars.
most ive run is 22 psi without a dump valve and that was on an xspower £100 to4e and that was fine !

ive heard on the ford forums that the gt series arent as strong as the old t series
 

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a dump valve is different to a blow off valve. this is a common mis-conception. i have to go now but if you research the 2 you will see the differences.

BOVs are sometimes incorrectly called dump valves because they serve a similar function, however they are very different solutions to the same problem.:thumbsup:

kev
 

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so why did nissan fit recirculating BOVs? if they do nothing to benefit the car then why bother? im not praising aftermarket BOVs im saying a pressure relief valve is fitted for a reason! would you recommend i just bung mine up?

kev
They're fitted for noise suppression. Imagine Saab, Volvo, Nissan, Porsche selling a turbo car to a 60 year old and when everytime he changes gears or backs off the right pedal it chatters like it's "broken"...
 

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researched.

the rally and race cars mentioned did not have pressure relief valves because they developed an anti lag system whereby the throttle is always held open thus allowing quick spool times, this is why rally cars 'pop' so much on gear change.

under massive boost levels, compressor wheels have been known to stop and even spin backwards. if compressor surge was no big deal then why would the race companies develop such an anti lag system.

kev
 

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lol, what can o'worms has been opened! Some good points raised, not sure there'll be one answer though :D
 
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